Generally, an organic EL device has the structure of a laminated luminescent part comprising an anode, a cathode, and an organic luminescent thin layer containing a fluorescent organic compound arranged between the two electrodes. In such an organic EL device, holes and electrons are injected into the fluorescent organic compound-containing thin layer, which recombine to generate exitons, and light (fluorescence, phosphorescence) is emitted when the generated exitons lose their excitation energy.
The biggest issue involved in the organic EL device is the enhancement of its operating life. One of various reasons causing decreased luminescent life is the appearance of non-luminescent dots referred to as “dark spots”, which tend to grow with the operating time to lower the brightness of the luminescent part. When such non-luminescent dots grow to the size of several 10 μm or larger, they can be recognized with the naked eye, which marks the end of the product life. It is known that such dark spots are generated and grow by the action of residual moisture or oxygen remaining inside the EL enclosed in a sealing case.
Consequently, it is necessary to remove moisture from inside of the sealing case of an organic EL device, and also to purify organic materials used in the luminescent part to remove moisture therefrom. In order to prevent moisture from remaining inside the sealing case, the processes of forming the luminescent part on a substrate plate in a vacuum chamber and sealing the substrate plate having the luminescent part with an enclosing cap are performed in an utmost dry state. However, it is not possible to completely eliminate moisture from said manufacturing processes, and therefore, the generation and growth of dark spots cannot be completely suppressed.
Thus, one of the most important problem to be solved in the field of organic EL device is how to prolong the use life by way of preventing the generation of dark spots or suppressing further growth of small dark spots. In this connection, an organic EL device comprising an inorganic drying agent disposed inside the sealing case is commercially available and disclosed, for example, in Japanese Publication No. 1997-148066 (‘Patent reference 1’).
Also, to solve the problem associated with the powder form of an inorganic drying means disclosed in Patent reference 1, Japanese Publication No. 2002-33187 (‘Patent reference 2’) teaches a technique of forming a layer of an organo-metallic compound having high reactivity toward moisture.
The organic EL device disclosed in Patent reference 2, as shown in FIG. 3, comprises an organic luminescent part having an organic luminescent layer (34) sandwiched between an anode (35) and a cathode (36) disposed on a glass substrate plate (32), wherein the organic luminescent layer (34) has a laminated structure of three layers comprising a hole injection layer (34a), a hole transport layer (34b) and a luminescent layer/electron transport layer (34c). The organic luminescent layer (34) is encased in a sealing case which consists of the glass substrate plate (32), an enclosing cap (33) and a sealing part (38), together with a water-scavenging agent layer (37) which protects the luminescent layer (34) from water. The water-scavenging agent layer (37) is a thin layer of an organo-metallic compound such as the compounds of formulae (III), (IV) and (V): 
The water-scavenging agent layer (37) may be obtained by dissolving the compound of formula (III), (IV) or (V) in an organic solvent and coating the solution on the inner surface of the enclosing cap (33) made of a flat glass plate to form a 10 μm thick film.
If necessary, the flat enclosing cap (33) is processed so as to form a 0.2 to 0.25 mm deep intaglio, or, as shown in FIG. 4, the enclosing cap (43) is manufactured in the form of an intagliated part (49), and a water-scavenging agent layer (47) is encased in the formed intaglio.
Conventional organo-metallic compounds which can be used to form the water-scavenging agent layer (37), e.g., the compounds of formulae (III), (IV) and (V), are dissolved in an organic solvent and the resulting solution is coated to form a film. Such compounds readily dissolve in a hydrocarbon-based solvent, but not in a polar solvent. Therefore, it is difficult to coat the conventional organo-metallic compounds by a screen printing method which requires the use of an acryl-based polymer dissolved in a polar solvent such as butylcarbitol and terpineol.